Ocean dredging is controversial. Environmentalists point to the harm that dredging can cause to marine ecosystems, but the practice is necessary to enable the safe, on-time arrival of vessels at ports all over the world.
Dredging must be performed on a semi-regular basis to keep waterways clear. In the waters surrounding England and Wales, 20 million tons of marine sand and gravel are dredged each year. It is likely that the frequency of these operations will only increase over time as the population and demand for infrastructure projects continues to grow.
We can’t stop marine dredging — the world’s commerce depends on ocean shipping — but we can invest in making ocean dredging safer and more efficient using ocean data. Let’s explore how.
What is ocean dredging?
Sea dredging or ocean dredging removes sediment from the sea and deposits it elsewhere. Ocean dredging is primarily used to create shipping channels or to maintain the depth of harbors. Dredging ensures that large vessels have the water depth needed to access routes and ports without running aground.
Dredging is also used for flood and storm protection, the extraction of mineral resources, and, in some cases, to support an ecosystem’s recovery following the contamination of sediments.
“This environmental dredging is often necessary because sediments in and around cities and industrial areas are frequently contaminated with a variety of pollutants,” said NOAA.
Pollutants in the ocean usually originate on land, meaning that sources like sewer overflow, surface runoff, and municipal or industrial discharge, can harm sediment.
Environmental dredging is a small percentage of dredging activity. Most often, ocean dredging is used to ensure that shipping operations continue without incident.
How does ocean dredging work?
Ocean dredging usually uses one of four main types of dredgers: cutter suction dredgers (CSDs), trailing suction hopper dredgers (TSHDs), grab dredgers, and backhoe dredgers.
CSDs and TSHDs are hydraulic dredgers and use suction to transfer material from the seabed to a hopper, barge, or pipeline. Cutter suction dredgers are usually used to remove hard substrates, while trailing suction hopper dredgers remove loose sediments while a vessel is in motion.
Grab and backhoe dredgers are mechanical dredgers and dig materials from an extraction site on the ocean floor. A grab dredger lowers a clamshell-like bucket to the sea floor, scooping material to be sorted at the surface on a barge. Backhoe dredgers use a similar bucket positioned at a vessel’s stern, which scoops materials to the surface to be sifted and sorted.
Consequences of sea dredging
Ocean dredging is damaging to the environment and can have a litany of negative impacts on sea flora and fauna.
“Physical injury or mortality from collisions, noise production, and increased turbidity are the main ways dredging can affect marine mammals directly,” according to an article in the ICES Journal of Marine Science.
“Indirect impacts on marine mammals from dredging stem from changes to their physical environment, or to their prey. Physical characteristics, such as topography, depth, waves, tidal currents, sediment particle size, and suspended sediment concentrations, are altered by dredging, but changes also occur naturally, as a result of disturbance events such as tides, waves, and storms.”
Dredging also can have a harmful impact on seagrasses, leading to long-term changes to the coastline that could potentially put onshore communities at risk. Seagrasses can help counter beach erosion and form part of a wave break, protecting the coast from storm surge. Dredging can expose seagrass beds to smothering, removal, or damage.
Fortunately, with the right data, we can limit the negative impacts of ocean dredging.
Ocean data's impact on dredging
Research shows that with the right management procedures in place, the effects of ocean dredging can be limited to sound masking, short-term behavioral alterations, and changes to prey availability.
Dredging contractors can use Sofar Ocean’s Spotter buoy and Smart Mooring to increase operational safety and efficiency. Operators can access the real-time wave data collected by Spotter to inform go/no-go decisions, as well as the subsurface water pressure data collected by Smart Mooring to monitor water level at the project site.
In the future, dredging contractors will also be able to use Sofar’s marine sensing devices to monitor turbidity, or how clear or opaque the ocean water is. Dredging stirs up a lot of sediment, leading to water turbidity measurements that are higher than usual (i.e. increased opacity). Turbid water is muddy, obscuring light and visibility for marine flora and fauna. With Spotter acting as a hub for power and connectivity, operators will be able to access measurements taken by a turbidity sensor affixed to Smart Mooring via the Bristlemouth open hardware interface, which provides plug-and-play functionality for marine sensing systems. This data, which is collected and transmitted in real-time, will enable ongoing turbidity monitoring during a dredging operation.
Interested in learning more about ocean data’s impact on dredging operations? Schedule a demo with our team.
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